"We've done all the (computer) modeling we could think of," Musk told CBS News on Monday. "In theory it should work."

The goal of the odd demonstration mission Musk has planned for Falcon Heavy starts with lift-off from Kennedy Space Center in Florida as early as 10:30 a.m. PT on Tuesday. If all goes well, it will end several hours later with a payload consisting of Musk's cherry red Tesla Roadster piloted by a space-suited dummy named "Star Man" pushed toward an elliptical orbit around Mars and Earth.

"Normally, when a new rocket is tested, they put something really boring on like a block of concrete or a chunk of steel or something," Musk said, explaining that SpaceX wanted to use a dead weight that might get the public more excited. "The car is just the most fun thing we could think of."

He estimates the Roadster will be in orbit for perhaps over a billion years with an "extremely tiny" chance it might someday hit Mars.

If it succeeds, the launch system will become the most powerful rocket in the world, second throughout history to only NASA's monstrous Saturn V, which sent Apollo astronauts to the moon.

For months, Musk has been actively lowering expectations that Falcon Heavy will succeed on its first try. On Monday, he guessed that the odds of success are between 50 and 70 percent.

Falcon Heavy is basically three Falcon 9 rockets strapped together and topped with a single second stage rocket. That means that at launch, a total of 27 engines will be firing at the same time right next to each other, something that has only been attempted before for just a few seconds during Falcon Heavy's hold-down firing test last month.

Heavy hitter

During the development of the Saturn V in the 1960s, early models of the rocket exploded during test firings just because of the acoustic vibrations generated by having multiple powerful engines next to each other. The solution to the problem that NASA came up with may seem counterintuitive for dealing with fiery rockets.

Humans on Mars: An atlas of plans to land on the Red Planet

"There are a lot of experts out there saying there's no way you can do 27 engines, all at the same time, and not have something go wrong," Musk said. "You've got the booster-to-booster interaction, acoustics and vibration that haven't been seen from any man-made device in a long time."

Tens of thousands are expected to flock to Florida Tuesday to try and catch a glimpse of the rocket thundering away from the same launch pad where Apollo astronauts left for the moon. Musk says he's confident they'll get a show of some kind.

"It's either going to be an exciting success or an exciting failure. One big boom! I'd say tune in, it's going to be worth your time."